The present invention relates to a method for bonding a slider and a suspension of a head gimbal assembly (hereafter referred to as an HG assembly) together, which is a component of a hard disk drive (HDD) unit. More particularly the invention relates to a method for fixing a slider and a suspension together temporarily when a low modulus epoxy adhesive is used for bonding said slider and said suspension together.
In prior art technologies, such a cyanoacrylate adhesive as an instantaneous adhesive or the like, have been used to bond sliders disposed at the tip of an HG assembly to a suspension. However, such an adhesive often causes the slider to be warped and/or distorted due to changes of the ambient temperature if the expansion coefficient differs between the slider and the suspension.
This warp and/or distortion, caused by an effect similar to that of bimetal, changes the xe2x80x9ccrownxe2x80x9d that indicates warping in the direction of the slider in which the air flows in and out, and/or the xe2x80x9ccamberxe2x80x9d that indicates warping in the direction orthogonal to that direction. Because this xe2x80x9ccrownxe2x80x9d and/or xe2x80x9ccamberxe2x80x9d affects the flying property of the slider significantly, the static posture of the HG assembly is changed unfavorably. Thus, a write head or read head disposed at the slider is disabled for writing/reading data in/from a disk.
To solve this problem, a low modulus epoxy adhesive has been used to absorb the difference of thermal expansion between materials with its own elasticity. The published but unexamined Japanese Patent Application No. 11-123488 by the present inventor discloses a method for bonding a slider and a suspension together with use of such an epoxy adhesive.
As shown in FIG. 6, this method uses a bonding jig 50 that will be described in greater detail below. A slider 25 is fixed to a slider mount 59 and an HG assembly 1 to which the slider 25 is not bonded yet is held on an HG assembly holding plate 51. In this state, a low modulus epoxy adhesive is dispensed on a bonding surface 25a of the slider 25, then the HG assembly holding plate 51 is rotated so that a flexure tongue 20 comes in contact with the bonding surface 25a. 
At this time, a locking hook 66 is fit in an engaging hole 67 and the flexure tongue 20 comes in contact with the bonding surface 25a, thereby the flexure tongue 20 is slightly more pressed against the bonding surface 25a. After that, a predetermined vibration is applied to this contact portion between the flexure tongue 20 and the bonding surface 25a so that both items 20 and 25a are bonded uniformly.
The low modulus epoxy adhesive employed here is a thermosetting adhesive, so the adhesive is heated and cured while the flexure tongue 20 is bound to the bonding surface 25a as described above so as to bond the flexure tongue 20 to the surface 25a. For example, the bonding jig that is holding the HG assembly is put in a controlled temperature chamber as described above, then it is exposed to a high temperature of 120xc2x0 C. for approximately 30 minutes. The flexure tongue 20 is thus fixed to the bonding surface 25a. This heating process may be carried out after the flexure tongue 20 is put in contact with the bonding surface 25a or more later, for example, in the final process.
However, in any of the above cases, the jig must be put in the controlled temperature chamber together with the HG assembly, so that the space in the controlled temperature chamber is not used so efficiently. In addition, because the jig is also heated, the thermal efficiency is not so high for the thermal capacity of the jig. If the heating process is carried out more later, both HG assembly and jig are moved from process to process, thereby more jigs are needed and the work efficiency is further lowered.
Under such circumstances, it is an object of the present invention to provide a method for bonding a slider and a suspension together, which enables the HG assembly bonded by a low modulus epoxy adhesive to be put in a controlled temperature chamber independently or moved from process to process, thereby improving the efficiency of the space usage in the controlled temperature chamber and the thermal efficiency so as to improve the work efficiency more.
A slider is joined to a suspension with a low modulus epoxy adhesive that is heated to cure the epoxy adhesive. A laser beam is applied to part of the adhesive for thermosetting the part while the slider and the suspension are held by a bonding jig so as to be pressed against each other with the low modulus epoxy adhesive therebetween. The laser beam may be applied to an opposite side where the suspension contacts the low modulus epoxy adhesive so that the beam axis of the laser beam hits the other side surface in an approximately vertical direction. The laser beam may be approximately 0.2 mm to 0.6 mm in diameter at its irradiation point if the slider is approximately 1.2 mm in length and 1 mm in width. The laser beam may be applied only at a predetermined output value and only for a predetermined time.
Furthermore, it is an object of the present invention to provide a method for bonding a slider and a suspension together, which includes a step for checking temperature properties of the resistance value of a head disposed at a slider. In addition, there is a step for detecting an ambient temperature of the head by measuring the resistance value so as to set both of the output value and the irradiation time of the laser beam. The output value and the irradiation time of the laser beam are decided so as to obtain a desired bonding strength of the low modulus epoxy adhesive through thermosetting of part of the adhesive by irradiation of the laser beam. within a predetermined upper limit temperature of the head. The resistance of the head may be a resistance of a write head coil.
When measuring the resistance, a four-wire ohm measurement should preferably be used to measure the resistance according to both of a constant current applied between a pair of pads formed at the slider so as to be connected electrically to the coil and a voltage measured between the pads.